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The Effect of 

Adding Zinc Oxide to 

Iron Oxide Paints 





Issued by 

The New Jersey Zinc Company 

(E»tat»liah«d 1848) 

160 Front Street, New York 

wg» s e g 

The Effect of 

Adding Zinc Oxide to 

Iron Oxide Paints 

Harley A. ^Nelson. M. V 

Chief of Pigment Research, Research Division 
I lie Ni-w Jersey Zin< I'ii Palmertoii Pa 

June 1929— Revised 


The New Jersey Zinc Conipan\ 

Established 1848) 

160 Front Street, Ntw York 

Products Distributed by 

The New Jersey Zinc Sales Company 

New 'Sork Chicago Pittsburgh * leveland San Francisco 


The Effect of 

Adding Zinc Oxide to 

Iron Oxide Paints 

Hv II \i;i \\ A. \ ELSON 

Introdi I HON 

A number of efforts have been made to classify pigments as to their 
desirable qualities for use in priming paints for metals thai are subject to 
corrosion. \s earl} as lo<> ( ) Smith 1 conducted a series of experiments 
designed to classify pigments according to their tendencies to pre\ent 
corrosion under the paint film. With the subsequenl developmenl of the 
rlntiulv ti< and other t heories of corrosion, investigators became increas- 
ingly interested in the probability that certain pigments could be definitely 
classed as inhibitors or stimulators of corrosion. The experiments described 
h\ < lushman and ( rardner represent tin' mosl extensive efforts to classify 
the then commercially available pigments. \ll of the more recenl tests on 
metal priming paints have shown the essential value of this infor- 
mation cannol be ignored, although when faced \sith the practicalities of 
paint manufacture cosl considerations or the lack of certain desirable 
properties in the individual pigments ma> limit its application. 


The investigators referred to above have all ranked Zinc Oxide as a 
pigmenl with definite rusl inhibitive properties. More recent work by H. 
Masseille has demonstrated the value of having zinc oxide next to the 
metal undei such extreme conditions as on ship-' bottoms. But, whatever 
[ts merits in this respect, it is also a well-known tact that zinc oxide 
impart \er> desirable properties t<» paint films. We ma> refer especially 
to the increased toughness and abrasive resistance of the film ; the incr< is< 
in original gloss and the greatei gloss retention, as well as the marked 
decrease in the chalking of paints in whi< h it is present. 

These advantages are a1 onceapparenl in finish coal paints and ari 
well known to n" ■ I t i i'i elabo ition at this time. However, the ad- 

iSmith I So< I h( '.i Im.I I>. (0 L89 
< orrosion ind Pr< 11 i \ ition ><t Iron and Steel page 169. 

II Masseille Department of Work ofFrenchNav^ Porl I roulon \ s on the oxidation ol 

huJla a nd th< • ■■ enting them from rust; Part II Causes thai facilitate Oi.- oxidation <>l metal 

hull- n-.- ..i / \i«l« -distemper as a preventative), Peintures, Pigments, Vernis Vol I No. 8, pages 3-6 . 

tugusl L924 


I Ml M VI |t KM \ /!%« < OMP4N1 

<i l»> using / li ki the common metal priming paints 

. fulls established, and ii is t I ol this papei t<. ^h<>v\ Iiom 

-I !»«• used in common t , I d priming paints to make 

ducts of paints tt mlj in- classed it best 

as in- | indpoint 

Iron "\ki ,|,|, in unlimited quantities at . i omparativel) Ion 

dities m bii b ha\ e mad< 
it popula mmI metal ed alone i-«i imm 

knesses vi hii h if the) \tuw been re< ognized 
n be oorrei U d Paint manu- 
■ ' ' n 1. 1. ra bli thought to the 

mat ' | , . : i.. . uned l'\ the additioi 

| III-I..U, . 

i in > hi i ii I ast be 
lint M - d in this country 

• •i 
m« lipjin rod ofl tra 

'i tof * bii h Mm. 

Id m ii h i hi. i 

* i iking!) i indii .t. d Ho* 

lit .-I /I! 

tint 1" )•' i 

i | 


im MMi 1 HI \IHHM. /!>.< OVIIIl Ml IKON U\II»h P\IM> 

but several iron o tiosen for comparison. These are listed in 

Table \n. hb> implex \.i- I to 7 in* lusive. 

The following priming punt- were made up with each iron oxide 
i l' LOO 4 i Iron Oxide 

I ;:v , Iron I bride 
- I IV, \\ Lead Free American Process Zinc Oxide 
j 75 lr< m I bride 
11 KX Lead 1 ree \ an Pi I nc Oxide 

Ordinary ' '^ linseed oil, turpentine and liquid drier vehicles were used 

\ll panels ivere exposed al i 45 ingle facing south on a hillside over- 
looking .hi industrial plant it Palmerton, Penna The moisture and sun- 
conditions were quite severe, and the tests are observed to 
be considerably a< I <>\ta similar paints in use on industrial plant 

sti nit in ee in i In- same localil ) 

rh( ' t tin- i»->i are tabulated in Table \o. 2, and partiall) illus- 

i l»\ representative photographs a> shown in Figures I t«> VIII. 
• • i h ii e more fullj discussed latei 

V r umber Two Exposed Vpril 7, I I 

I in test was designed t«» supplement the experiment dr>< ribrd above, 
and to further pro\ e that it is essential to have the /im uxufr bearing paint 
him next to t Im- metal. 

I'm ivith four iron oxides Samples 9, I". 13 

i ii fable I), both without zin< oxide and with 15^j rin< * r < J i - 

tck Iron panels 12 inches b> -' I inches 22 - divided 

- 1 i< 1 1 1 \ in inn sections 

i. ft li ind section was primed with tin Iron Oxide-15* , /im 

Oxide [Mint Hie right ha in I section w.(- primed « it h LOO Iron Oxide 

P unt. 

\\ hi -hU Hi ied the 1 1 ■ »n ' tatide-Zinc ( '\id»> section vs . i 

finish coal oi cunt >»i l"<» Iron Oxide, ami tl '\ide 

section was finished with in 85 Iron Oxide and 15 Zin< Oxide] 

panels were exposed ii ui ingle ol 15 nth. 

results ol this test are tabulated in I ible \ I ind 
illustrated hv the photographs, Figures l\ ind \ 

• ret I \p- ised \pi \\ I 

\ third test iras 
fable No. 1 I bese p inela • 

INK NK.W JERSE1 /l\< c mil'Wt 

Tesl Number One, excepl that for one panrl <>t .,,, h se1 the vehicle in the 
8595 [ronCbride -l.V, Zinc Oxide paint was modified by adding 20 b) 
_ht of a high grade spar varnish. The results are tabulated in Tal l< 

I. and partially illustrated l>\ tl iphs shown as Figures \l 

and XII. 

// should be noted tfiat the metal panels used in this tesl. as well G 
Number Tun. were of a common grade black iron, which is a a 
infi ■ <>n in rust resistance as compared with the metals used in 

\ umber One. described above. This should be htrne in mind by I 

/ ring the d n the types of corrosion appearing on the panels. 


The panels in each test were first graded indep -nd.-ritU I 
who divided them into groups according to their relative condition, 
sample, it was n.mid that the p erall) fell into five distinct 

ps ranging from extreme!) or vei I condition. This 

sification is indicated in Tal N _ • d 1. 

Panels in Figures I and II are shown in col 

the existing color differences, wh I I- obtained 

the ordinary photographs. The othei panels photograph 
furtl tive exhibits chosen with th< i illustrat 

the • Lained b) adding zinc • I the desirabil 

the zinc oxide next to the metal. The panels seta U d I 
are indicated in the Tables \>\ references to the figure aumJ 

I III III xlifllNt. /IN< l»\ll»l Ml IKllN (IMIII- I'UNh 

- / 

1 - 




tn - 


— . — ' 



— ~~ 


a " 


/ - 


a a 

' 7 5 

= - 

3r* — ~ 

s — 1 1 1 1 

a * " 

' - a SLTS ~ - - 

' a aaafl -— — 

" jt r — - 

£ - - X X 

<osa;aSflC«QS / / x 

— - — c 


-- — 

! i — 3 - i 5i i - - i i ■ . 

X C S 

— C C C i — 


■ — ex — >-i-3xr = ri-3 



_~r-=-I / 2^2 




_ _ -^ 





nil dim i 01 I HG ZIN< OXIDI in IRON oxini- i*\ini^ 










I III \l U It KM \ /|N< < *t\\rw\ 



12^ 12 








Figure I 
(See Page L2 

Photograph of panel No. 7 (Test Nuinb: , r One. Series Mo, 7) primed 
with Iron i )\ide No. :\ i Ho isted ( arbonate), without ;m\ added zinc oxide. 
Rated with Group I as being in very poor condition (See Table No. 2). 

>n " \" : (One coat of priming paint.) Rusting general. Paint 

entirelx <rone. 

-m "£": (Two coats of priming paint.) Rusting is general. Paint 
practically all disappeared from surface. 

(One coat of priming paint plus two coats of a gre^ finish 
paint.) Rusting and \<t> b.idh checked and cracked. 

This photograph is primarily intended to aid the reader in gaining a 
i i .-till*, ini.-. .nd itini i ot the panels as shown in the ordinary 
photographs that follow. It should be compared with the ordinary photo- 
graph, Figure III, and contrasted with Figure fl showing a colored photo- 
graph of the same iron oxide with t .7 , zinc oxide added. 


I II) M W |l HM ^ /I N< « OMI'VN^ 


Mil Mill I Ol \lll»l\«. /1N< 0\ll>h IO IKON u\ll>l- l'\|Nh 


Figure II 

Colored Photograph of Groi p V, Series 7, No. 8 

(See pap- I I 



Figure III 
page 16) 

Photograph of panel No. 7 (Tesl Number One, Series No. 7 primed with 
Iron Oxide No. 3 (Roasted Carbonate) without any added zinc oxide. 
Rated with Group I as being in very poor condition (see Table No. - 

This is a photograph of the same panel shown in Figure I. and is in- 
tended to illustrate the ordinary photographic reproduction of the colors. 
The photograph should be contrasted with Figure IV, showing the same 
iron oxide with l.V " ( Zinc Oxide added. 



I M I M« I I I ( - I > / I v 

THE EFFE4 I OK \M>I\<, /IN< 0\II>K TO IRO\ o\n»t PVINTS 

Figure IV 

See page 18) 


It M U II H-l "> / I M 


I 7 

fit \\ 



Figure V 
(See Page 20 

Photograph of panel No. t (Test Number One, Series No. 6) primed 
with Iron Oxide No. 2 Mineral Brown) without zinc oxide. Rated with 
Group I as being in very poor condition (see Table V 

Section \ One coat of priming [taint onlx.i Badl> rioted and paint 

all gone. 

Section "£"; (Two coats of priming paint.) Badly rusted and paint 
practically all gone. 

Section "C": (One coat primer and two coats of a gre> finish paint.) 
Badly spotted with rust pits. Severe checking and cracking 

over entire >ui fare. 

I hi- photograph should be contrasted with Figure \ 1 I he panel is in 
the same general condition as Fig. I and Figure III, and direct comparisons 
of these photogi nph> should be made to get the significance of the darker 

areas on (lie ordinal \ photographs. 




it • 

Fit; i hy: VI 
, 22) 

I lit M \* II KM 1 /l\< f OMPAN1 

I" K.I RE \ I 

page 2 1 

Photograph of panel No. 5 (Tesl Numbei One, Series No. 6) primed 
with [ron Oxide No. 2 < Mineral Brown with IV by weighl \ \ "Ameri- 
can Process" Zinc Oxide. Rated with Group \ as being in i - good con- 
dition see Table V 

Section " \" (( hie coal <»i' priming paint. Rusting through film in spots 
hut over 50 ( { of paint film inta< I and ^till giving protection 
to the metal. Note absence <»i extremt col Qtrasl 

be!\\ - • ii ,riv " V and 1 1 

Section "B : (Tin oi priming paint. V ver$ f< w localized m^i 

spots. Film in excellent condition. 

Section "C One coal of primer plus two i finish paint. 

\ few localized rust spots showing through the painl film. 

Slight chedkii it. In ex< ellent condi- 

tph should be i ontrasted « itfa I igure \ show ing the same 
iron oxide uitlmui zinc oxide added. 


Figure VII 
Se< Page 24 

Photograph of panel No. L3 Tes1 Number One, Series No. 7) primed 
with Iron Oxide No. 6 mixture of Canadian and Spanish) without zinc 
oxide. Rated with I iroup I as being in very poor condition (see Table No. 2). 
Section "A": One coal of priming paint.) Badl} rusted and paint en- 

lnrly £OIK\ 

Sectioi I. Two coats of priming paint.) Badl> rusted and paint 

almost entirely jrone. 

Section "C"; (One coat of primer and two mats of a gre> finish paint.) 
Badly spotted with rust pits. Severe checking and cracking 
over entire surface. 
This photograph should be contrasted with Figure VIII, which shows 

the same iron oxide with l.V \ Zinc < >xide added. 




THE EFFECT OF Vl»l»IN<- /IN« OXIDE TO IKON OXtlth l*\l\l^ 


Fkhke VIII 


Figure IX 

(See Page 28) 

Photograph of panel No. 25 (Test Number Two) with Iron Oxide No. 9 
i Venetian Red) as follows: (See Table No. 3. ) 

Section "A": Priming coat containing 15% (by weighl \\ American 
Process" Zinc Oxide; second coat is same iron oxide without 
any zinc oxide.) Note absence of any rust pits on this sur- 
face. Film in excellent condition throughout. Rated as 
being in very good condition. 

lion "B": (Priming coat contains no zinc oxide; second coat contains 
l.V , Zinc Oxide as described above.) Note prevalence of 
rust pits on Section "B", some of which have developed ex- 
tensively. The paint film is breaking down rapidly. Rated 
as being in poor condition. 

This photograph illustrates results with a good grade of iron oxide 
(compare with Figure X). 




Figure X 
See page 30) 




Figure XI 
- Pajrr32) 

Photograph <>l" imm.'I \.». P) 'Test Number Three) primed with Inm 
Oxide No. II Red Oxide without an\ zinc oxide. Rated as being in 
extremely poor condition see I able No. I . 

Section "A": (One coal of priming paint. 

on "B": (Two coats of priming paint.) 

Section "C" One coat oi priming paint plus two coats of a gre> Qnish 
coat p mit Note the extreme checking of the finish coat 


This photograph should be compared with Figure Ml showing the 
same iron oxide with zinc oxide added. 

The attention of the readei is again i ailed to tin- pitted type of corro- 

>inn which is i\piral <»(' t fie ordinary black iron used in Test Number Three. 



THE KFFK( I i*h tl>l»|M. /INC 0\ll>K IO IKON OXIIH-. POINTS 

i 1 

Figure XII 

(See pa^e 3 1 1 

Mil inn I o| ADDING /IN< OXID1 Hi ll<o\ o\n»| PAINT* 

Disci ssion oi Results 

The outstanding fact broughl ou1 f>\ the tests i^ that in ever} i 
w it 1 1 i tut a single exception, the addition of zinc oxide has greatly impro\ ed 
the quality "I tin- priming paints. The inspection data indicates thai the 
useful life of the paint films has at leasl been doubled, and in some cases 
im reased even more 

Examination of the panels shows thai this improvemenl becomes evi- 
dent in at leasl two important respect I irst, it has rit her gxeatl> reduced 
or practically eliminated tin- tendency to pitting due to corrosion under t h>- 
priming film: second, it has decreased the tendency of the finish painl to 
check and alligat n 

The firsl of* these can, of course, onl} be ascribed to definite increase 
in the protei 1 i\<- <pialit> of the film, whethei this is due to inhihitive prop- 
erties of zinc oxide itself, to a neutralization of acidic compounds in the 
film by zinc oxide, or to a general increasing of the imperviousness of tin- 
punt film to gasses and moisture. The results of Tes1 Number Ty 
peciall} emphasize the necessity for having the zinc oxide in tin' film 
nexl to thr metal. 

I he universal de< rease in the i heckingof the finish paints over the zinc 
oxide bearing films can be ascribed to the well known hardening action of 
/im oxide. This is in accord with th< generally accepted principle that, if 
i he< king and alligatoring are to \>< avoided, tfn- priming painl miM nol 
remain softei than the coats subsequently applied. 

Except in the case of the Venetian Red Panel No 7) the relative ad- 
vantage of adding more than l ixide to iron oxides is nol at all 
[nop. .1 tionate to the Improvement up to l.V , zinc oxide. It seems probable 
that the optimum amount of zinc oxide, for most practical purposes, is from 
l". to20 b} weighl of the pigment portion of the paint. 

I M t-pi in .1 fi-w individual cases the differences between the iron oxides 
themselves are nol of the same ordei oi magnitude as the differences in 
qualit> introduced h\ adding zinc oxide. If an\ conclusions are to be 
drawn concerning I In- iron oxides the} would be I that the \er> high 
Fe*0 bearing iron oxides Indian Reds ire not suited for use in metal 
priming paints 2 that even a moderate! content may not, in 

itself, be an indication of outstanding properties for use in metal priming 
paints; '» that, while individual Venetian Reds ma) _ri\e fair results, 



• 4 

'</'» Sim4mnl Jed*